The invention relates to a method of monitoring the safety of a respirator with an endotracheal tube, whereby at least one jet nozzle supplied by a respiratory gas source and a measuring tube terminate in the vicinity of the distal end of the tube, the measuring tube shutting off the respiratory gas source through a pressure sensor and a switch if the pressure exceeds a preset limit. In addition, a plurality of devices are provided in which the method can be worked advantageously.
Respirators which permit HFPPV (high frequency positive pressure ventilation) are known for respiration or assisting respiration. For example, according to German OS No. 28 47 681, an endotracheal tube is used for this purpose which has at its distal end two jet nozzles and one sampling tube supplied by a respiratory gas source at overpressure, by which the monitoring processes can be carried out.
The respiratory gas stream emerging from the jet nozzles has a driving pressure of 1-5 bars. The incoming volume of gas is largely independent of the impedance of the lungs. If the expiratory pathway (main lumen) becomes blocked above the jet oulet point, an inadmissibly high over pressure will develop in the bronchi in a relative short period of time (approximately 20 to 40 seconds). In general, this can cause rupturing and severe damage to the lungs. Blockage of the expiratory pathway can occur in various ways, for example, by accumulation of secretion or kinking of the endotracheal tube resulting in blockage of the expiratory pathway while gas continues to be supplied at high pressure.
To avoid these disadvantages, it is already known from German OS No. 28 34 037 to dispose a sampling or sensing tube in the air flow and monitor the pressure prevailing therein in this fashion. When an inadmissibly high overpressure is detected, the respiratory gas source is disconnected by an appropriate indirectly controlled switching mechanism. However, a design of this type offers no guarentee against kinking and/or plugging of the sampling or sensing tube, because in this case the normal pressure prevailing at a given moment will be stored, and the switching mechanism will not operate to shut off the respiratory gas flow despite and instant pressure rise in the airways.